1. Field of the Invention
The present invention relates to a honeycomb filter.
2. Description of the Related Art
A honeycomb filter has been proposed that has a porous structure in which, when cell partitions have a first pore group of pores having a diameter in the range of 1.0 to 150 μm and a second pore group of pores having a diameter in the range of 0.006 μm or more and less than 1.0 μm in a pore distribution curve, a single peak of the pore diameter distribution is present in the first pore group and a plurality of peaks of the pore diameter distribution are present in the second pore group (for example, refer to Patent Literature 1). It is stated that this filter can achieve trapping and removing of particulate matter (PM) contained in exhaust gas and cleaning of hazardous gas. Another honeycomb filter has been proposed that has partitions having porous partition bases and surface layers provided on the inflow sides of the partition bases, wherein conditions including the peak pore diameter of the surface layers, the porosity of the surface layers, the thickness of the surface layers, the mass of the surface layers with respect to filtration area, and the average pore diameter of the partition bases are properly adjusted (for example, refer to Patent Literature 2). In this filter, a rapid increase in the pressure loss immediately after the initiation of trapping of particulate matter (PM) is not caused and the relationship between the amount of PM deposited and the pressure loss does not have hysteresis characteristics. Thus, the pressure loss in an initial state where PM is not deposited can be suppressed to a low value.    Patent Literature 1: WO2006/041174    Patent Literature 2: WO2008/136232